Isotope effect in charge transport of LuB12

Abstract

The galvanomagnetic properties of single-crystal samples with various isotopic boron compositions have been investigated for the first time for the normal state of superconductor LuB12 (T c ≈ 0.44 K). Precision measurements of the resistivity, Hall coefficient, and magnetic susceptibility have been performed over a wide temperature range of 2–300 K in magnetic fields up to 80 kOe. A change of the charge transport regime in this nonmagnetic compound with metallic conduction is shown to occur near T* ≈ 50−70 K. As a result, a sharp peak with significantly different amplitudes for Lu10B12 and Lu11B12 is recorded in the temperature dependences of the Hall coefficient R H(T) near T*. A significant (about 10%) difference (in absolute value) of the Hall coefficients R H for the Lu10B12 and Lu11B12 compounds at helium and intermediate temperatures has been found and the patterns of behavior of the dependence R H(H) for T < T* in an external magnetic field H ≤ 80 kOe for Lu10B12 and Lu11B12 are shown to differ significantly. Analysis of the Curie-Weiss contribution to the magnetic susceptibility χ(T) leads to the conclusion about the formation of magnetic moments μeff ≈ (0.13−0.19)μB in each unit cell of the fcc structure of LuB12 compounds with various isotopic compositions. The possibility of the realization of an electronic topological 2.5-order transition near T* and the influence of correlation effects in the 5d-band on the formation of a spin polarization near the rare-earth ions in LuB12 is discussed.